1. Field of the Invention
The present invention relates to a plasma display panel (PDP). More specifically, the present invention relates to an apparatus and a method for displaying gray scales of a PDP, which are capable of reducing the generation of flickering and a pseudo-outline during the displaying of gray scales of a moving picture.
2. Description of the Related Art
A PDP is a kind of a display device for recovering input picture data from an electric signal by arranging a plurality of discharge cells in the form of a matrix and selectively radiating the discharge cells.
The PDP can display gray scales so as to function as a color display device. A gray scale display method for dividing a field into a plurality of sub-fields with time divisions controlling the sub-fields is used.
In a common gray scale display method, the number of sub-fields is fixed regardless of video data. In a method for displaying gray scales using a variable sub-field method, the number of sub-fields is determined according to the average signal level (ASL) of a video signal of one field. Input video data are mapped and stored in a field memory according to the determined number of sub-fields. Because the ASL is determined only when all of the video data of a field are input, a field memory for storing the data is necessary while the ASL of continuously input video data is determined. Therefore, the continuously input video data are mapped by sub-field by the ASL determined in a previous field and are stored in the field memory. The data stored in the field memory are read in a next field and are sustained according to the currently determined ASL.
FIG. 1 is a block diagram of a gray display apparatus using a variable sub-field method in a conventional PDP.
As shown in FIG. 1, the gray scale display apparatus using the variable sub-field method includes a video signal processor 10, a gamma correction and error diffusion unit 20, an automatic power controller 30, first and second field memories 40 and 50, a sub-field generator 60, first and second frame memories 70 and 80, an address data generator 90, and a sustain scan pulse generator 100.
The video signal processor 10 digitalizes a video signal input received from the outside and generates digital video data.
The gamma correction and error diffusion unit 20 receives the digital video data output from the video signal processor 10, corrects a gamma value according to the characteristics of a PDP 110, diffuses a display error with respect to peripheral pixels, and outputs the digital video data.
The automatic power controller 30 selectively stores the video data output from the gamma correction and error diffusion unit 20 in the first and second field memories 40 and 50 according to whether the video data are even field data or odd field data, and detects the ASL of the respective video data. The ASL can be determined after the video data are stored in the field memories 40 and 50.
The sub-field generator 60 selectively stores the video data output from the automatic power controller 30 in the first and second frame memories 70 and 80 and generates gray scale data corresponding to the respective video data.
The address data generator 90 generates address data corresponding to the gray scale data output from the sub-field generator 60 and applies the address data to the address electrodes A1, A2, . . . and Am of the PDP 110.
The sustain scan pulse generator 100 receives the ASL output from the automatic power controller 30, generates sustain pulses and scan pulses, and applies the sustain pulses and the scan pulses to the scan electrodes X1, X2, . . . and Xn and to the sustain electrodes Y1, Y2, . . . and Yn of the PDP 110.
FIG. 2 schematically shows a method for displaying gray scales using a variable sub-field method in a conventional PDP.
As shown in FIGS. 1 and 2, (n−1)th field data Dn−1 is input to the first field memory 40 through the automatic power controller 30 in a (n−1)th field. The ASL of the (n−1)th field data Dn−1, that is, ASLn−1, is determined by the automatic power controller 30 at the point of time when the input of the (n−1)th field data Dn−1 is completed, that is, when the (n−1)th field data Dn−1 is stored in the first field memory 40. ASLn, that is, the ASL of nth field data Dn, and ASLn+1, that is, the ASL of (n+1)th field data Dn+1, are determined by the method used for determining the ASLn−1.
The field data Dn−1, Dn, and Dn+1 are divided into even field data and odd field data and are alternately stored in the first field memory 40 and the second field memory 50. The field data Dn−1, Dn, and Dn+1 are sub-field mapped by the ASL determined in a previous field by the sub-field generator 60 and are stored in the corresponding frame memories 70 and 80.
For example, the nth field data Dn is sub-field mapped according to the number of sub-fields, which is determined by the ASLn−1 determined in the (n−1)th field, and is stored in the first frame memory 70. The (n+1)th field data Dn+1 is sub-field mapped according to the number of sub-fields, which is determined by the ASLn determined in the nth field, and is stored in the second frame memory 80.
In each field, data stored in a previous field are read and a sustain operation is performed on the PDP 110 according to the number of sub-fields, which is determined by the ASL determined in the previous field.
For example, in the nth field, the (n−1)th field data Dn−1 stored in the first frame memory 70 is read from the (n−1)th field and the sustain operation is performed according to the number of sub-fields, which is determined by the ASLn−1 determined in the (n−1)th field. In the (n+1)th field, the nth field data Dn stored in the second frame memory 80 is read from the nth field and the sustain operation is performed according to the number of sub-fields, which is determined by the ASLn determined in the nth field.
With reference to the nth field data Dn stored in the second frame memory 80 in the nth field, meanwhile, the second frame memory 80 is sub-field mapped according to the number of sub-fields determined by the ASL determined in the (n−1)th field that is a previous field, that is, the ASLn−1, and the sustain operation is performed in the (n+1)th field. Therefore, the sustain operation is performed according to the number of sub-fields, which is determined by the ASL determined in a previous field, that is, the ASLn.
In the variable sub-field method, the sub-field mapping is performed in a different way according to the ASL of the video data. For example, when the ASL is 33, 10 sub-fields are mapped. When the ASL is 34, 11 sub-fields are mapped, and so on. This is depicted in FIGS. 3 and 4.
In the variable sub-field method, when the ASL of an adjacent pixel corresponds to the boundary where the sub-field mapping varies, that is, the ASLs of adjacent pixels are 33 and 34 with reference to the above example, (see FIGS. 3 and 4) the ASL applied when the field memory is stored is different from the ASL applied when the sustain operation is performed on the field data. Accordingly, an undesirable screen flickering phenomenon occurs.